In industries producing vaccines by means of cell culture or producing biological substances secreted either by adherent or suspension cells or by micro-organisms, use is made of microcarriers, roller bottles, Roux flasks, multiple chamber systems and fermentors.
Microcarriers are small microscopic beads on which adherent cells are caused to grow. The beads are maintained in suspension in the culture medium, hereafter called the liquid phase, with the help of a stirring system, the liquid phase being in contact with a gas phase. Everything is contained in a tank called fermentor. This technique frequently used in the vaccine industry is nonetheless confronted with two major difficulties:
the difficulty of carrying out a suspension of micro-carriers in the culture medium which is compatible with anchorage and cell growth conditions, PA1 the difficulty of ensuring the control and stability of the culture medium pH, when taking into account the fact that the exchange surface between the gas phase and the liquid phase is substantially limited.
Fermentors are also used for the culture of suspension cells or micro-organisms. The handling difficulties are similar to those encountered during cultivation with a microcarrier; as the exchange surface between the gas phase and the liquid phase is limited by the fermentor diameter, the pH stability becomes extremely difficult to ensure.
Roller bottles are generally of cylindric shape and are designed to be rotatable around their axes. The interior surfaces of these bottles are foreseen for cultivating adherent cells thereby forming culture surfaces. The liquid of culture is introduced into the bottle together with the cells. The rotating movement to which the bottles are subject, allows the culture surfaces to be covered with a film of medium thereby allowing cell growth on these culture surfaces. The culture surface is therefore limited to the size of the bottles. If the production of a large quantity of cells is desired, a large number of bottles will be necessary. This is the case for industries producing, for example, interferon, insulin, viral vaccines, lymphokines. The handling of these numerous bottles during inoculation, medium change, virus introduction, supernatant and cell harvesting increases the risk of bottle and content contamination and requires the use of an important number of staff. Many apparatus have been developed in order to increase the culture surface of roller bottles by increasing the surface of the bottle itself. These known apparatus are intended for developing adherent cell culture but are not foreseen for providing a homogeneous suspension of microcarriers or of suspension cells.
Roux flasks have been used for more than a century for producing viruses, as well as other biological substances. They have the same drawbacks as roller bottles, that is to say a limited culture surface per bottle and they require an important number of handling staff.
Document EP-A-0345415 discloses an apparatus in which the bottle has an enlarged surface. This enlargement of the surface is obtained by providing the bottle body with a corrugated surface having corrugations which extend axially or longitudinally relative to the bottle axis. This bottle does not, however, allow liquid stirring. Therefore it does not permit cultivation with microcarriers.
The surface used for cell development is also increased with the apparatus disclosed in document U.S. Pat. No. 3,839,155. With this apparatus, additional surface is obtained with a parallel arrangement of trays along the bottle axis. This apparatus however is not entirely satisfactory for adherent cells because the trays, when in a horizontal position, cannot retain a volume of liquid containing the cell suspension. This causes the liquid to run out of the tray which does not favour cell attachment during cultivation. Moreover, this apparatus is not appropriate for the cultivation of so-called non-adherent cells because nothing is provided here for stirring of the liquid phase.
Document LU-A-51646 describes a cell culture apparatus comprising Of a set of parallel trays placed one above the other so as to form culture chambers. All of this is placed inside the housing which can be rotatable around an axis. This system permits cultivation of adherent cells on one side of the trays only. The interior surface of the housing is not used as a culture surface. Moreover, a stirring system allowing the microcarriers or micro-organisms to be maintained in homogeneous and continuous suspension, cannot be introduced.